Conventional steel roller and conveyor-chains are made by alternately joining together an inner link subassembly comprising an inner link plate and a bush pressed therein and an outer link subassembly comprising an outer link plate and a pin pressed therein. When these chains are subjected to tensile load, bending and shearing stresses are exerted on the pin and bush, while tensile stress is applied on the link plates. Particularly, the perforated portion of the link plates where the pin or bush is inserted yields under such tensile stress, thereby giving rise to plastic deformation. Because of this, the engaging force between the outer link plate and the pin and the inner link plate and the bush is reduced, and engagement therebetween is liable to be loosened. Such reduction in engaging force and loose engagement lower the durability of the chain and cause such damages as fatigue and wear rupture of the link plates, pin and bush. To improve the fatigue strength (dynamic strength) of a chain, the following mechanical measures are generally taken:
1. Improvement of paralleledness and machining accuracy of the perforated portion of the link plate.
2. Chamfering of the hole in the link plate.
3. Increase of engaging force between the link plate and the pin or bush through the increase of interference therebetween.
4. Pre-exertion of residual compressive stress on the perforated portion of the link plate.
Despite the adoption of these methods, the dynamic performance of the chain is reduced in actual use by the loosening of engagement under the influence of thermal stress occurring under the actual operating condition, atmosphere in use, suitability of machine work, and other factors. Therefore, these are not the perfect measures to improve fatigue strength.
In an effort to improve the dynamic strength of conventional steel roller chains, the link plates have often been welded to the respective pins and bushes by welding techniques utilizing a filler material, such as the well-known arc-welding technique. However, the resulting chains produced using filler-type welds between the link plates and the respective pins or bushes have not provided any significant increase in the strength and durability of the chain, particularly as regards the dynamic or fatigue strength characteristics.
Accordingly, the object of the present invention is to provide a substantially improved roller chain which utilizes a fillerless fusion weld between the link plate and the respective pins or bushes, which fillerless weld results in the chain having substantially increased dynamic strength characteristics.
Specifically, the present invention proposes to render the inner link plates and the bushes, and the outer link plates and the pins, into a complete integral body by welding their total engaged surfaces together by means of a precision welding technique, specifically electron beam welding, or laser welding, thereby providing a fillerless fusion weld along the total engaged surfaces of the respective elements while producing extremely little deformation.